1. Field of the Invention
This invention relates to a bismuth (Bi) substituted garnet among optical garnet materials having a Faraday rotation effect and a manufacturing method thereof and, more specifically, to a single crystal thick film of GdBi series garnet grown by a liquid phase growing method and a manufacturing method thereof.
2. Statement of Related Art
Heretofore, devices based on the Faraday rotation effect have been developed and put into practical use in the light communication or optical information processing. In light communication apparatus using semiconductor laser oscillators, when reflection light from optical fiber cables or connectors return to laser oscillation portions, noises increase to make the oscillators. Therefore, an optical isolator utilizing the Faraday rotation effect has been used in order to ensure oscillation the state by shutting return light.
Bi substituted type rare earth garnets having a large Faraday rotation effect been grown by an LEP method, flux method or the like and used for isolators in near infrared regions.
Particularly, since garnet thick films grown by the LPE method are excellent in productivity, most of the garnet thick films have been produced by this method at present.
At present, in communication systems using optical fiber cables, wavelength bands from 1.31 xcexcm to 1.55 xcexcm and, further, from 1.6 to 2 xcexcm have been utilized.
As the material for Faraday rotation devices for near infrared regions used in such wavelength bands, TbBi series garnet thick films and GdBi series (Ga or Al-substituted) garnet thick films prepared by the LPE method have been marketed.
The former material has a small temperature variation coefficient of the Faraday rotation per 45 deg as about 0.04 to 0.06 deg/xc2x0 C. but the application magnetic field intensity Hs is as high as about 800 to 1200 Oe to require a powerful permanent magnet. The material has a magnetization inversion temperature of about xe2x88x9250xc2x0 C. or lower and can be used in a wide temperature range.
On the other hand, the latter material has a large temperature variation coefficient of the Faraday rotation per 45 deg as about 0.08 deg/xc2x0 C., Hs is as small as about 300 Oe, the magnetization inversion temperature is as high as about xe2x88x9210xc2x0 C. and the working temperature range is near the life environmental temperature.
Accordingly, market""s demand has been increased for TbBi series garnet materials having satisfactory temperature characteristics.
However, for rare earth Bi series garnet materials, absorption spectrum attributable to Tb ions appears in a region of a wavelength of 1.6 xcexcm or longer, as shown in the chart of a literature entitled as xe2x80x9cEffect of Impurities on the Optical Properties of Yttrium Iron Garnetxe2x80x9d in the Journal of Applied Physics, Vol. 38, No. 3, pp. 1038, and increase of transmission loss in this wavelength region is inevitable in the TbBi garnet material.
On the other hand, for GdBi series (Ga, Al-substituted) garnet thick film, the manufacturing conditions are shown in the literature entitled as xe2x80x9cLPE Growth of Bismuth Substituted Gadolinim Gadonium Iron Garnet Layers: Systematization of Experimental Resultxe2x80x9d in the Journal of Crystal Growth 64 (1983), p. 275, but the literature does not suggest the GdBi series (Yb, Al-substituted) garnet thick film.
It is desirable that the optical isolator shows higher transmittance in the advancing direction and lower transmittance in the direction opposite thereto.
In view of the above, it is an object of this invention to provide a material for bismuth-substituted garnet thick film capable of avoiding light absorption at a wavelength of about 1.6 xcexcm inherent to the TbBi series garnet and improving the temperature variation coefficient of the Faraday rotation effect of the GdBi series garnet, as well as a manufacturing method thereof.
It is another object of this invention to reduce the cost by using commercially available substituted gadolinium-gallium-garnet (SGGG) substrate of a large grown substrate diameter.
It is still another object of this invention to provide a Faraday rotation device used in a wavelength region in excess of about 1.5 xcexckm.
According to one aspect of this invention, there is provided a material for a bismuth substituted garnet thick film which comprises Gd, Yb, Bi, Fe and Al as the main ingredient grown by a liquid phase growing method on a garnet substrate in which the composition of the garnet thick film is represented by the general formula:
Gd3-x-yYbxBiyFe5-zAl2O12
(0 less than xxe2x89xa60.5, 0.85xe2x89xa6yxe2x89xa61.55 and 0.15xe2x89xa6zxe2x89xa60.65), and each of boron oxide (B2O3) and lead oxide (PbO) is contained by from 0 to 4.0 wt % (not including 0) in the garnet thick film.
According to another aspect of this invention, there is provided a Faraday rotation device which comprises substantially a garnet thick film comprising Gd, Yb, Bi, Fe and Al as the main ingredient grown by a liquid phase growing method on a garnet substrate. In the Faraday reotation device, the composition of the garnet thick film is represented by the general formula:
Gd3-x-yYbxBiyFe5-zAl2O12
(0 less than xxe2x89xa60.5, 0.85xe2x89xa6yxe2x89xa61.55 and 0.15xe2x89xa6zxe2x89xa60.65), and each of boron oxide (B2O3) and lead oxide (PbO) is contained by from 0 to 4.0 wt % (not including 0) in the garnet thick film.
According to still another aspect of this invention, there is provided a method of manufacturing a material for bismuth substituted garnet thick film of growing a garnet thick film comprising Gd, Yb, Bi, Fe and Al by a liquid phase growing method on a garnet substrate. In the present invention, the method includes growing the garnet thick film on a substituted gadoliniumxe2x80x94galliumxe2x80x94garnet (SGGG) substrate and the composition of the garnet thick film is represented by the general formula:
Gd3-x-yYbxBiyFe5-zAl2O12
(0 less than xxe2x89xa60.5, 0.85xe2x89xa6yxe2x89xa61.55 and 0.15xe2x89xa6zxe2x89xa60.65), and each of boron oxide (B2O3) and lead oxide (PbO) is contained by from 0 to 4.0 wt % (not including 0) in the garnet thick film.